The present invention relates to a magnetic recording and reproducing apparatus (hereinafter referred to as the "VTR") of a high picture quality pursuing type provided with an automatic tracking control system.
FIG. 12 is a diagram schematically illustrating a configuration of an automatic tracking control system of a conventional VTR disclosed in, for instance, Japanese Patent Publication No. 51256/1980 or 51257/1980.
In the drawing of FIG. 12, reference numeral 1 denotes a magnetic tape. Written on the magnetic tape 1 are video tracks 2 with video signals recorded thereon as well as control tracks 3 on which control signals used for tracking servo during reproduction are recorded. Magnetic heads 4A, 4B, which are used for reproducing the video signals, are mounted on a rotating drum 6. The rotating drum 6 is rotated at a predetermined speed by a drum motor 8 through control by a drum motor drive circuit 7. A fixed control head 5 is adapted to reproduce control signals.
A frequency generator 10 generates a frequency signal (hereinafter referred to as the FG signal) proportional to the rotating speed. The magnetic tape 1 is driven in the direction of arrow a via a pulley 12, a belt 13, and a capstan 14 by a capstan motor (hereinafter referred to as the CP motor) 9 whose drive is controlled by a capstan motor drive controlling circuit (hereafter referred to as the CP motor drive controlling circuit ) 11.
A control amplifier 16 amplifies the control signal, and a phase comparator 17 receives as one of its inputs the control signal amplified by the amplifier 16. A phase adjusting circuit 20 adjusts the phase of a rotational phase signal obtained by detecting a magnetic piece 18 affixed to the rotating drum 6 by means of a fixed detection head 19, i.e., a rotational angle signal of the two magnetic heads 4A, 4B. This phase adjusted signal is used as the other input for the phase comparator 17. An error signal of the phase comparator 17 is applied to the CP motor drive controlling circuit 11.
A video FM signal reproduced by the magnetic heads 4A, 4B is fetched by a rotary transformer 21, and is then amplified by a head amplifier 22 and supplied to an envelope detection circuit 23. An output of the head amplifier 22 is also supplied to a peak hold circuit 24 which holds a maximum value V.sub.p of an envelope signal. An envelope detection signal V.sub.e which is an output of the envelope detection circuit 23 and the output signal V.sub.p of the peak hold circuit 24 are applied to a comparator 25.
The output of the comparator 25 is supplied to a differential circuit 26. A flip-flop circuit 27 generates an output voltage polarity of positive and negative by means of an output of the differential circuit 26. An integration circuit 28 integrates the output of the flip-flop circuit 27 and controls the phase of the phase adjusting circuit 20 in correspondence with its output polarity.
The operation of the above-described configuration will be described hereinunder.
The CP motor 9 is driven and controlled as the FG signal generated by the frequency generator 10 is applied to the CP motor drive controlling circuit 11. The magnetic tape 1 is hence driven in the direction of arrow a in FIG. 12 via the pulley 12, the belt 13, and the capstan 14, and the drum motor 8 is rotatively driven at a predetermined rotating speed via the drum motor drive circuit 7. At this time, the control signal reproduced by the control head 5 and amplified by the control signal amplifier 16 is applied to one input terminal of the phase comparator 17. At the same time, the signal phase-adjusted by the phase adjusting circuit 20 by means of the rotational phase signal obtained by detecting the magnetic piece 18 affixed to the rotating drum 6 by means of the detection head 19 is applied to the other input terminal of the phase comparator 17.
The error signal out of the phase comparator 17 is applied to the CP motor drive controlling circuit 11 so as to finely control the CP motor 9 being driven at a speed in the vicinity of a substantially predetermined speed by this drive controlling circuit 11, thereby controlling the travel of the magnetic tape 1 such that the rotational phase of the magnetic heads 4A, 4B and the reproduction phase of the control signal assume the relationships of phase determined by the phase adjusting circuit 20. As a result, the magnetic heads 4A, 4B scan fixed relative positions of the tracks 2 for the video signals determined by the phase adjusting circuit 20.
Meanwhile, the video FM signal reproduced by the magnetic heads 4A, 4B is fetched by the rotary transformer 21 and is then amplified by the head amplifier 22 and input to the envelope detection circuit 23, where the detected envelope signal is applied to the comparator 25.
The output of the head amplifier 22 is also applied to the peak hold circuit 24, and the output of this peak hold circuit 24 and the output of the envelope detection circuit 33 are supplied to the comparator 25. The comparator 25 makes a comparison between the output voltage V.sub.p of the peak hold circuit 24 and the output voltage V.sub.e of the envelope detection circuit 23, and determines whether a voltage differential between them is smaller than a threshold e.sub.0 which has been appropriately set.
Then, the output of the comparator is supplied to the differential circuit 26 which generates positive and negative pulses each time the output of the comparator 25 is reversed. The flip-flop circuit 27 is triggered only by the negative pulses of the differential circuit 26, thereby changing its state between positive and negative voltage levels. The output of the flip-flop circuit 27 is supplied to the integration circuit 28 so as to be subjected to integration. Thus the output of the flip-flop circuit 27 is converted to a signal corresponding to the output voltage polarity of the flip-flop circuit 27 in order to control the phase of the phase adjusting circuit 20.
Now, if it assumed that the phase of the phase adjusting circuit 20 is in the state of a shown in FIG. 13, that the output voltage of the flip-flop circuit 27 is at a positive voltage level, and that the output of the integration circuit 28 is in an increasing direction, the phase of the phase adjusting circuit 20 changes in the increasing direction of b and then toward c. Concurrently, the output of the envelope detecting circuit 23 gradually increases and then assumes a decreasing direction again after reaching a maximum envelope value indicated by a broken line 30 in FIG. 13. Accordingly, because when the phase of the phase adjusting circuit 20 is set in the state of d, the difference between the output voltage V.sub.e of the envelope detecting circuit 23 and the output voltage V.sub.p max of the peak hold circuit 24, i.e., the maximum envelope voltage indicated by the broken line 30 in FIG. 13, becomes the predetermined threshold value e.sub.0 of the comparator 25 indicated by a broken line 31 in FIG. 13. Accordingly, the comparator 25 shifts from the positive level to the negative level, with the result that the differential circuit 26 generates a negative pulse, thereby causing the flip-flop circuit 27 to shift to the negative voltage level. Consequently, the output of the integration circuit 28 begins to decrease, and the phase of the phase adjusting circuit 20 decreases again, shifting in the direction from d to c.
As described above, tracking adjustment is carried out by effecting control such that as the phase of the phase adjusting circuit 20 fluctuates from b to d, the output voltage of the envelope detecting circuit 23 fluctuates between the voltage levels indicated by the broken lines 30 and 31, and by setting the threshold value e.sub.0 to an appropriate level.
The conventional VTR is arranged as described above, and coordination between the control signal and the positions in which the magnetic heads jump in (or jump out) is controlled. Hence, although the automatic tracking function is accomplished in cases where the recorded tracks are rectilinear, as shown in FIG. 5(a), in cases where the recorded state of the recorded video tracks is poor and the tracks are curved, as shown in FIG. 5(b), it is impossible for the magnetic heads to follow the field tracks having such curves. Thus there has been a problem in that the above-described arrangement is insufficient as a tracking function of a VTR for which high-quality pictures are pursued.